TweetFollow Us on Twitter

Mar 97 Getting Started

Volume Number: 13 (1997)
Issue Number: 3
Column Tag: Getting Started

An Expanded ShapeWorld Applet

By Dave Mark

Last month's Getting Started column introduced the ShapeWorld applet. The initial version of ShapeWorld featured four classes: The ShapeWorld class extends the Applet class and creates and controls all the applet objects. The ShapeCanvas class extends the Canvas class and implements the canvas we'll do all our drawing in. The Shape class is designed to be extended and provides the basic functions for implementing a shape. The RectShape class extends Shape and overrides the Shape classes' abstract draw() method to draw a rectangular shape.

Why divide the shapes into two separate classes? After all, we could have just done the drawing in the Shape class. However, that is what this month's column is all about. We are going to add a second Shape subclass to our applet, along with some code that lets you drag your shapes around in the ShapeCanvas.

The ShapeWorld Project

Here's the source code to this month's applet. For the most part, we've added code to last month's project with only a few lines changed (mostly to change the way highlighting works - more on this in a moment).

import java.awt.*;
import java.util.*;

abstract class Shape
{
 booleanhighlighted;
 ShapeCanvasshapeCanvas;
 int    shapeX, shapeY, shapeWidth, shapeHeight;
 RectangleboundsRect;
 
 Shape( ShapeCanvas canv, int x, int y,
 int width, int height )
 {
 shapeCanvas = canv;
 highlighted = false;
 
 shapeX = x;
 shapeY = y;
 shapeWidth = width;
 shapeHeight = height;
 
 boundsRect = new Rectangle( x, y, width, height );
 }
 
 abstract public void draw( Graphics g );
 
 public void erase( Graphics g )
 {
 g.clearRect( shapeX, shapeY, shapeWidth, shapeHeight );
 }
 
 public void setHighlight( boolean newHighlight )
 {
 highlighted = newHighlight;
 }
 
 public boolean isHighlighted()
 {
 return highlighted;
 }
 
 public boolean isPointInShape( int x, int y )
 {
 return boundsRect.inside( x, y );
 }

 public voidmoveThisMuch( int x, int y )
 {
 boundsRect.move( shapeX + x, shapeY + y );
 shapeX = boundsRect.x;
 shapeY = boundsRect.y;
 shapeWidth = boundsRect.width;
 shapeHeight = boundsRect.height;
 }
}

class RectShape extends Shape
{
 RectShape( ShapeCanvas canv, int x, int y,
 int width, int height )
 {
 super( canv, x, y, width, height );
 }
 
 public void draw( Graphics g )
 {
 if ( isHighlighted() )
 {
 g.setColor( Color.black );
 g.fillRect( shapeX, shapeY, shapeWidth, shapeHeight );
 g.setColor( Color.red );
 g.fillRect( shapeX+2, shapeY+2,
 shapeWidth-4, shapeHeight-4 );
 }
 else
 {
 g.setColor( Color.red );
 g.fillRect( shapeX, shapeY, shapeWidth, shapeHeight );
 }
 }
}

class OvalShape extends Shape
{
 OvalShape( ShapeCanvas canv, int x, int y, int width,
 int height )
 {
 super( canv, x, y, width, height );
 }
 
 public void draw( Graphics g )
 {
 if ( isHighlighted() )
 {
 g.setColor( Color.black );
 g.fillOval( shapeX, shapeY, shapeWidth, shapeHeight );
 g.setColor( Color.red );
 g.fillOval( shapeX+2, shapeY+2,
 shapeWidth-4, shapeHeight-4 );
 }
 else
 {
 g.setColor( Color.red );
 g.fillOval( shapeX, shapeY, shapeWidth, shapeHeight );
 }
 }
}

class ShapeCanvas extends Canvas
{
 Vector shapes;
 Shape  curShape;
 Point  mousePosition;
 
 ShapeCanvas( int width, int height )
 {
 shapes = new Vector();
 curShape = null;
 
 setBackground( Color.yellow );
 
 resize( width, height );
 }
 
 public void addShape( Shape newShape )
 {
 shapes.addElement( newShape );
 }
 
 public void paint( Graphics g )
 {
 for ( Enumeration e = shapes.elements(); 
 e.hasMoreElements(); )
 {
 Shape s = (Shape)e.nextElement();
 s.draw( g );
 }
 }
 
 public Shape findInShapeList( int x, int y )
 {
 for ( Enumeration e = shapes.elements(); 
 e.hasMoreElements(); )
 {
 Shape s = (Shape)e.nextElement();
 
 if ( s.isPointInShape( x, y ) )
 {
 s.draw( getGraphics() );
 
 return s;
 }
 }
 
 return null;
 }
 

 public void update (Graphics g)
 {
   paint(g);
 }
 
 public boolean mouseDown( Event e, int x, int y )
 {
 curShape = findInShapeList( x, y );
 
 if ( curShape != null )
 {
 curShape.setHighlight( true );
 mousePosition = new Point( x, y );
 
 return true;
 }
 
 return false;
 }
 
 public boolean mouseDrag( Event e, int x, int y )
 {
 Graphics g;
 
 if ( curShape != null )
 {
 g = getGraphics();
 
 curShape.erase( g );
 
 curShape.moveThisMuch( x - mousePosition.x,
 y - mousePosition.y );
 
 mousePosition.x = x;
 mousePosition.y = y;
 
 curShape.draw( g );
 
 return true;
 }
 
 return false;
 }
 
 public boolean mouseUp( Event e, int x, int y )
 {
 if ( curShape != null )
 {
 curShape.setHighlight( false );
 repaint();
 
 return true;  
 }
 
 return false;
 }
}

public class ShapeWorld extends java.applet.Applet
{
 ShapeCanvassCanvas;
 final intshapeWidth = 20;
 final intshapeHeight = 20;
 
 public void init()
 {
 int    x, y;
 
 sCanvas = new ShapeCanvas( 440, 290 );
 add( sCanvas );
 
 Random ran = new Random();
 Rectangle b = sCanvas.bounds();
 
 for ( int i=1; i<=10; i++ )
 {
 x = b.x + (int)((float)(b.width) * ran.nextFloat() );
 if ( x > b.x + b.width - shapeWidth )
 x -= shapeWidth;
 
 y = b.y + (int)((float)(b.height) * ran.nextFloat() );
 if ( y > b.y + b.height - shapeHeight )
 y -= shapeHeight;
 
 RectShape r = new RectShape( sCanvas, x, y, 
 shapeWidth, shapeHeight );
 sCanvas.addShape( r );
 }

 for ( int i=1; i<=10; i++ )
 {
 x = b.x + (int)((float)(b.width) * ran.nextFloat() );
 if ( x > b.x + b.width - shapeWidth )
 x -= shapeWidth;
 
 y = b.y + (int)((float)(b.height) * ran.nextFloat() );
 if ( y > b.y + b.height - shapeHeight )
 y -= shapeHeight;
 
 OvalShape r = new OvalShape( sCanvas, x, y, 
 shapeWidth, shapeHeight );
 sCanvas.addShape( r );
 }
 }
}

Running the New ShapeWorld

Before we get to the source code differences between last month's applet and this month's applet, take a look at Figure 1, which shows the applet running under the Metrowerks VM. The figure shows the applet window with the ShapeCanvas taking up most of the window (shown in yellow). The Canvas shows 10 RectShapes and 10 OvalShapes.

Notice that only one shape is highlighted. In last month's applet, we toggled highlighting for a shape on and off again with each click. Since we added dragging this month, I wanted to try a slightly different approach to highlighting. Now, highlighting turns on when a drag starts and turns off when the drag ends. This isn't necessarily correct for all applications, but the changes needed to implement this approach are worth understanding.

Notice also that when one shape drags over another, the underlying shape is erased to the background color and is not restored until the drag ends. Take some time to see why this happens. How could you change this code so that "dragged-over" shapes are not erased by the drag?

Figure 1. The new ShapeWorld applet running under the Metrowerks VM.

What Source Code was Added This Month?

The first change made to last month's code is the addition of 2 new methods to the Shape class. erase() calls the Graphics method clearRect() to erase the current Shape to the background color. As you might guess, erase() is a key part of the erase/redraw cycle we use when dragging a shape. This is definitely a bare-bones approach to drag animation. Can you come up with some alternatives?

 public void erase( Graphics g )
 {
 g.clearRect( shapeX, shapeY, shapeWidth, shapeHeight );
 }

moveThisMuch() takes an x and a y offset and moves the shape that many pixels left or right and up or down. Just a reminder: since we maintain both a Rectangle (boundsRect) and a set of individual x, y, width, and height variables, we'll need to update both. On reflection, if I had this to do over again, I probably would have picked one or the other but not both, just to avoid the confusion that comes with having to keep both in sync.

 public voidmoveThisMuch( int x, int y )
 {
 boundsRect.move( shapeX + x, shapeY + y );
 shapeX = boundsRect.x;
 shapeY = boundsRect.y;
 shapeWidth = boundsRect.width;
 shapeHeight = boundsRect.height;
 }

Next, we added a new Shape subclass. OvalShape is almost identical to RectShape, calling fillOval() instead of fillRect(). Though the OvalShapes may look like circles, they are indeed ovals. Try changing the bounding rectangle used to create them and see for yourself.

class OvalShape extends Shape
{
 OvalShape( ShapeCanvas canv, int x, int y, int width,
 int height )
 {
 super( canv, x, y, width, height );
 }
 
 public void draw( Graphics g )
 {
 if ( isHighlighted() )
 {
 g.setColor( Color.black );
 g.fillOval( shapeX, shapeY, shapeWidth, shapeHeight );
 g.setColor( Color.red );
 g.fillOval( shapeX+2, shapeY+2,
 shapeWidth-4, shapeHeight-4 );
 }
 else
 {
 g.setColor( Color.red );
 g.fillOval( shapeX, shapeY, shapeWidth, shapeHeight );
 }
 }
}

Next, the variable mousePosition was added to the ShapeCanvas class. mousePosition is used to track the mouse's position when the drag started and as it proceeds.

class ShapeCanvas extends Canvas
{
 Vector shapes;
 Shape  curShape;
 Point  mousePosition;

To implement the drag, we had to make a few changes. First, we added some code to the mouseDown() method to highlight the shape and store away the current mouse position.

 public boolean mouseDown( Event e, int x, int y )
 {
 curShape = findInShapeList( x, y );
 
 if ( curShape != null )
 {
 curShape.setHighlight( true );
 mousePosition = new Point( x, y );
 
 return true;
 }
 
 return false;
 }

While the drag is happening, we'll get repeated calls to mouseDrag(). Assuming the drag was inside a shape, we first erase the shape, then move it, then redraw it.

 public boolean mouseDrag( Event e, int x, int y )
 {
 Graphics g;
 
 if ( curShape != null )
 {
 g = getGraphics();
 
 curShape.erase( g );
 
 curShape.moveThisMuch( x - mousePosition.x,
 y - mousePosition.y );
 
 mousePosition.x = x;
 mousePosition.y = y;
 
 curShape.draw( g );
 
 return true;
 }
 
 return false;
 }

When the mouse button is released, the mouseUp() method is called. When this happens, we unhighlight the shape and redraw all the shapes. Note the difference between repaint() and draw().

 public boolean mouseUp( Event e, int x, int y )
 {
 if ( curShape != null )
 {
 curShape.setHighlight( false );
 repaint();
 
 return true;  
 }
 
 return false;
 }
}

Finally, we'll add some code to the ShapeWorld class to create 10 of our new OvalShapes. This code is the same as that used to create the RectShapes.

 for ( int i=1; i<=10; i++ )
 {
 x = b.x + (int)((float)(b.width) * ran.nextFloat() );
 if ( x > b.x + b.width - shapeWidth )
 x -= shapeWidth;
 
 y = b.y + (int)((float)(b.height) * ran.nextFloat() );
 if ( y > b.y + b.height - shapeHeight )
 y -= shapeHeight;
 
 OvalShape r = new OvalShape( sCanvas, x, y, 
 shapeWidth, shapeHeight );
 sCanvas.addShape( r );
 }

Till Next Month...

Take some time to look over this code. Can you improve it? What happens if you replace the erase() call with a call to repaint()? Can you improve the performance of the code? How would you add a graphical background to the Canvas? Can you add a pair of buttons to the interface, one to create a new RectShape and one to create a new OvalShape at a random location in the Canvas? See you next month.

 
AAPL
$100.86
Apple Inc.
-0.77
MSFT
$46.76
Microsoft Corpora
+0.52
GOOG
$579.95
Google Inc.
+6.85

MacTech Search:
Community Search:

Software Updates via MacUpdate

Capture One Pro 8.0.0.433 - RAW workflow...
Capture One Pro 8 is a professional RAW converter offering you ultimate image quality with accurate colors and incredible detail from more than 300 high-end cameras -- straight out of the box. It... Read more
Adobe Acrobat Pro 11.0.09 - Powerful PDF...
Adobe Acrobat allows users to communicate and collaborate more effectively and securely. Unify a wide range of content in a single organized PDF Portfolio. Collaborate through electronic document... Read more
Adobe Reader 11.0.09 - View PDF document...
Adobe Reader allows users to view PDF documents. You may not know what a PDF file is, but you've probably come across one at some point. PDF files are used by companies and even the IRS to... Read more
iFFmpeg 4.6.1 - Convert multimedia files...
iFFmpeg is a graphical front-end for FFmpeg, a command-line tool used to convert multimedia files between formats. The command line instructions can be very hard to master/understand, so iFFmpeg does... Read more
NTFS 11.3.62 - Provides full read and wr...
Paragon NTFS breaks down the barriers between Windows and OS X. Paragon NTFS effectively solves the communication problems between the Mac system and NTFS, providing full read and write access to... Read more
OS X Yosemite 10.10 DP8 - Developer Prev...
Note: This is a Developer Preview. You must be a registered Apple Mac Developer to download this update. You can also sign up for the free OS X Beta Program to download and preview public beta... Read more
FotoMagico 4.5 - Powerful slideshow crea...
FotoMagico lets you create professional slideshows from your photos and music with just a few, simple mouse clicks. It sports a very clean and intuitive yet powerful user interface. High image... Read more
Screenshot Path 1.2.1 - Change the defau...
Screenshot Path lets you change the folder where OS X saves screenshots. Screenshots are saved by default to the user’s desktop. This is handy for the occasional screenshot but those looking to take... Read more
Fantastical 1.3.16 - Create calendar eve...
Fantastical is the Mac calendar you'll actually enjoy using. Creating an event with Fantastical is quick, easy, and fun: Open Fantastical with a single click or keystroke Type in your event details... Read more
GIMP 2.8.14 - Powerful, free image editi...
GIMP is a multi-platform photo manipulation tool. GIMP is an acronym for GNU Image Manipulation Program. The GIMP is suitable for a variety of image manipulation tasks, including photo retouching,... Read more

Latest Forum Discussions

See All

Zynga Unveils First Look at Looney Tunes...
Zynga Unveils First Look at Looney Tunes Dash! Posted by Ellis Spice on September 16th, 2014 [ permalink ] Be vewy, vewy qwiet. I’m hunting wunners featuwing wabbits, and luckily, it’s duck season wunner season. | Read more »
Guardians on the Go – How to Connect to...
At this point I’m relatively certain most of the country is familiar with Destiny. And for those looking to augment their game a bit, Bungie has changed their Bungie Mobile Companion App to Destiny Companion. | Read more »
Kunin Review
Kunin Review By Jordan Minor on September 16th, 2014 Our Rating: :: SHURIKEN DO ITUniversal App - Designed for iPhone and iPad Kunin is a nervous test of ninja reflexes.   Developer: Dodreams Price: FREE Version Reviewed: 1.0.1... | Read more »
4 KEMCO Titles are Just $0.99 for a Limi...
4 KEMCO Titles are Just $0.99 for a Limited Time Posted by Jessica Fisher on September 16th, 2014 [ permalink ] KEMCO RPGs Destiny Fantasia, Infinite Dunamis, Bonds of the Sk | Read more »
Introducing Flash, the Latest Wearable F...
Introducing Flash, the Latest Wearable Fitness Monitor from Misfit Posted by Jessica Fisher on September 16th, 2014 [ permalink ] The Misfit Flash is the newly-released fitness and sleep monitor from | Read more »
Hyper Trip Review
Hyper Trip Review By Jennifer Allen on September 16th, 2014 Our Rating: :: HYPER TWITCHYUniversal App - Designed for iPhone and iPad Tough and unforgiving, Hyper Trip is a bit like Snake – if Snake was really harsh.   | Read more »
Collectible Card Game Earthcore: Shatter...
Collectible Card Game Earthcore: Shattered Elements is Set to Arrive on iOS in 2015 Posted by Ellis Spice on September 16th, 2014 [ permalink ] Polish developers | Read more »
Boogey Boy Review
Boogey Boy Review By Jennifer Allen on September 16th, 2014 Our Rating: :: PRETTY BUT BASICUniversal App - Designed for iPhone and iPad It looks delightful but lack of Game Center support and more variety really affects the fun... | Read more »
Vizzywig 4K (Photography)
Vizzywig 4K 1.0 Device: iOS iPhone Category: Photography Price: $999.99, Version: 1.0 (iTunes) Description: REQUIRES: iOS 7 on iPhone 5S with 32GB or 64GB. (Do not use iOS 8)The world's FIRST mobile 4K video capture, editing and... | Read more »
The Sleeping Prince Review
The Sleeping Prince Review By Jennifer Allen on September 15th, 2014 Our Rating: :: RESTRICTIVE KINGDOM SAVINGUniversal App - Designed for iPhone and iPad The Sleeping Prince looks and feels great to play, but its lack of peril and... | Read more »

Price Scanner via MacPrices.net

Sprint offers 16GB iPad mini for $199.99 with...
Sprint is offering 1st generation 16GB iPad minis for $199.99 with a 2-year service agreement. Standard MSRP for this iPad is $429. Their price is the lowest available for this model. Read more
2.5GHz Mac mini remains on sale for $549, sav...
B&H Photo has the 2.5GHz Mac mini on sale for $549.99 including free shipping. That’s $50 off MSRP, and B&H will also include a free copy of Parallels Desktop software. NY sales tax only. Read more
Apple refurbished iMacs available for up to $...
The Apple Store has Apple Certified Refurbished iMacs available for up to $300 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. These are the best prices on... Read more
13″ 2.5GHz MacBook Pro offered for $100 off M...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999.99 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
Free GIMP Professional Grade Graphics App Ver...
The latest 2.8.14 version of the oddly-named GIMP (acronym for: GNU Image Manipulation Program) open source, high-end image editing and creation alternative to Adobe’s Photoshop and refuge from... Read more
Apple Announces Record Pre-orders for iPhone...
Apple has released metrics showing a record number of first day pre-orders of iPhone 6 and iPhone 6 Plus, with over four million sold in the first 24 hours. Demand for the new iPhones exceeds the... Read more
10% off iPhone 6 and 6 Plus Otterbox cases
Get 10% off on popular Otterbox iPhone 6 and iPhone 6 Plus cases at MacMall through September 19th. Use code OTTERBOX10 to see the discount. Read more
15-inch MacBook Pros on sale for up to $125 o...
Amazon has the new 2014 15″ Retina MacBook Pros on sale for up to $125 off MSRP including free shipping: - 15″ 2.2GHz Retina MacBook Pro: $1899.99 save $100 - 15″ 2.5GHz Retina MacBook Pro: $2374... Read more
27-inch 3.2GHz iMac on sale for $1698, $101 o...
Abt has the 27″ 3.2GHz iMac on sale for $1698 including free shipping. Their price is $101 off MSRP. Read more
More To Making A Larger iPad Than Expanded Sc...
CNET’s Ross Rubin has posted a thoughtful analysis of prospects for a larger display iPad Pro, noting that Microsoft and Samsung currently have the large-display touchscreen tablet category to... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.